The vast nebula NGC 604 above in the Triangulum galaxy is a Hubble Space Telescope image. Though such nebulae are common in galaxies, this one is nearly 1,500 light-years across -so vast it is easily seen in ground-based telescopes. At the heart of NGC 604 are over 200 hot stars, much more massive than our Sun.

The young stars heat the gaseous walls of the nebula making the gas flouresce. Their light also illuminates the nebula's three-dimensional shape. By studying the physical structure of a giant nebula, astronomers may determine how clusters of massive stars affect the evolution of the interstellar medium of the galaxy. The nebula also yields clues to the starburst process when a galaxy undergoes a "firestorm" of star formation.

This new image below from NASA's Spitzer Space Telescope shows M33, the Triangulum Galaxy located about 2.9 million light-years away in the constellation Triangulum, in all its glory. The galaxy is a member of what's known as our Local Group of galaxies. Along with our own Milky Way, this group travels through the universe together in gravitaional bondage.

M33 is one of the few galaxies that is moving toward the Milky Way despite the fact that space itself is expanding, causing most galaxies in the universe to grow farther and farther apart.

Stars appear as glistening blue gems (several of which are actually foreground stars in our own galaxy), while dust rich in organic molecules glows green. The diffuse orange-red glowing areas indicate star-forming regions, while small red flecks outside the spiral disk of M33 are most likely distant background galaxies. With its ability to detect cold, dark dust, Spitzer can see emission from cooler material well beyond the visible range of M33's disk. Exactly how this cold material moved outward from the galaxy is still a mystery, but winds from giant stars or supernovas may be responsible.